Voltage Drop

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wattup

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I need to maintain no more than a 3% voltage drop with the following information. Can you tell me what wire size to run using THHN?
Single phase with neutral feeder to 100 amp panel ( assume they want to load it to the max.) Voltage is 208 and the footage is 550 feet.
 
By 'load it to the max', are you assuming 100A of line to neutral loading on each leg, 80A of line to neutral loading on each leg, or 80A of line to line loading at 208V? Is it safe to assume that this 'single phase' panel is really two legs tapped from a 208/120V three phase supply?

Also, are the motor loads or other loads with high starting current which might momentarily exceed the panel rating for short periods of time?

-Jon
 
wattup said:
I need to maintain no more than a 3% voltage drop with the following information. Can you tell me what wire size to run using THHN?
Single phase with neutral feeder to 100 amp panel ( assume they want to load it to the max.) Voltage is 208 and the footage is 550 feet.
Click to expand...


No way to answer that question with that info..We all know what assume really means..
 
When the circuit conductors have already been installed, the voltage drop of the conductors can be determined by using one of the following formulas:

VD = 2 x K x Q x I x D/CM - Single Phase

VD = 1.732 x K x Q x I x D/CM - Three Phase

“VD” = Volts Dropped: The voltage drop of the circuit conductors as expressed in volts.

“K” = Direct Current Constant: This is a constant that represents the direct current resistance for a one thousand circular mils conductor that is one thousand feet long, at an operating temperature of 75? C. The direct current constant value to be used for copper is 12.9 ohms and 21.2 ohms is used for aluminum conductors. The “K” constant is suitable for alternating current circuits, where the conductors do not exceed No. 1/0.

“Q” = Alternating Current Adjustment Factor: Alternating current circuits No. 2/0 and larger must be adjusted for the effects of self-induction (skin effect). The "Q" adjustment factor is determined by dividing alternating current resistance as listed in NEC Chapter 9, Table 9, by the direct current resistance as listed in Chapter 9, Table 8.

“I” = Amperes: The load in amperes at 100 percent, not 125 percent for motors or continuous loads.

“D” = Distance: The distance the load is located from the power supply, not the total length of the circuit conductors.

“CM” = Circular-Mils: The circular mils of the circuit conductor as listed in Chapter 9, Table 8.
 
wattup said:
I need to maintain no more than a 3% voltage drop with the following information. Can you tell me what wire size to run using THHN?
Single phase with neutral feeder to 100 amp panel ( assume they want to load it to the max.) Voltage is 208 and the footage is 550 feet.
Click to expand...
It's a good question but information is vague. Thhn is a type of insulation.
 
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